Alarm systems are important devices in monitoring systems or control systems of a technical plant, such as power plants or production plants, for example, and are an important aid for assisting operating personnel in detecting plant or process states which may require immediate intervention. The method of operation of the alarm systems for determining and displaying plant or process states is determined by alarm parameters, for example, by defined limit values of process variables.
Analyses carried out following an occurrence of serious malfunctions have shown the importance of the quality of alarm systems or optimum alarm parameters. It has come to light in this case that both late reporting of faults which were already looming a relatively long time beforehand and an excessively large number of alarm signals may be problematic. A single process fault, such as blocked valve, for example, may result in many different subsequent alarms, for example “flow rate too low” or “filling level too low”. It is not unusual for the same process fault to result in hundreds of alarms. However, only those alarms to which the plant operators are capable of actionably reacting should be reported to the plant operators. In addition, the total number of alarms reported should also remain limited in critical situations since a large number of reports can not only be annoying but dangerous as well since, on the one hand, the personnel's attention maybe diminished and, on the other hand, important reports may be overlooked and/or ignored.
The findings from such analyses have resulted both in guidelines and recommendations for alarm systems and in multifarious attempts by experts to suppress undesirable reports and optimize alarm parameters. For example, EEMUA 191 (The Electrical Equipment Manufacturers and Users Association guide, publication No. 191, 1999, ISBN 0 85931 076 0) mentions that it is also expedient to limit the reported alarms to a total number of ten alarms within ten minutes for critical situations in an attempt to prevent plant operators from being overtaxed by the multiplicity of alarms. To achieve such aims, causal relationships between alarms are analyzed and a distinction is made between causal alarms (root cause) and subsequent alarms. An alarm identified as a subsequent alarm can be suppressed by means of suitable mechanisms in the control system. U.S. Pat. No. 5,581,242 proposes, for example, the practice of working with tables which store conditions for suppressing the display of generated alarms. WO 2006000110 describes a method for suppressing redundant alarms, in which a filter is used to identify those alarms from previously generated alarms which are redundant and those which have not yet been classified. Only non-redundant alarms and alarms which have not yet been classified are displayed. In addition, alarm management tools are commercially available. Such tools can be used, for example, to calculate correlation coefficients between alarms and may be a basis for configuring alarm suppression rules. However, only binary data, such as alarm on or off, are used in this case and results have, overall, been unsatisfactory. Plant operators occasionally consider alarm systems to be so useless or disruptive that they prefer to ignore them.